U.S. patent application number 13/046988 was filed with the patent office on 2011-09-29 for method for evaluating reliability of electrical power measuring device.
This patent application is currently assigned to DAIHEN CORPORATION. Invention is credited to Ryohei TANAKA.
Application Number | 20110238360 13/046988 |
Document ID | / |
Family ID | 44657358 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110238360 |
Kind Code |
A1 |
TANAKA; Ryohei |
September 29, 2011 |
METHOD FOR EVALUATING RELIABILITY OF ELECTRICAL POWER MEASURING
DEVICE
Abstract
A method is provided for evaluating the reliability of an
electrical power measuring device for measuring high-frequency
electrical power. To build an evaluation system, the measuring
device, together with a reference electrical power measuring
device, is arranged between a high-frequency power supply device
and an artificial reproduction load, which includes an impedance
conversion device and a reference load. Using this system, an
uncertainty range of an electrical power measured value measured by
the measuring device is calculated, according to a prescribed
calculation formula, from the electrical power measured value, and
a judgment is made as to whether or not the electrical power
measured value measured by the measuring device is within the
uncertainty range. If it is within the uncertainty range, the
measuring device is evaluated as being reliable, while if it is not
within the uncertainty range, the measuring device is evaluated as
being unreliable.
Inventors: |
TANAKA; Ryohei; (Osaka,
JP) |
Assignee: |
DAIHEN CORPORATION
Osaka
JP
|
Family ID: |
44657358 |
Appl. No.: |
13/046988 |
Filed: |
March 14, 2011 |
Current U.S.
Class: |
702/116 |
Current CPC
Class: |
G01R 21/06 20130101;
G01R 21/01 20130101; G01R 35/04 20130101; G01R 35/005 20130101;
G01R 35/00 20130101 |
Class at
Publication: |
702/116 |
International
Class: |
G06F 19/00 20110101
G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2010 |
JP |
2010-065652 |
Claims
1. A method for evaluating the reliability of an electrical power
measuring, device that is connected to a connection point between a
high-frequency power supply device and a load having a complex
impedance, the electrical power measuring device being configured
to measure high-frequency electrical power at the connection point,
the method comprising: terminating a transmission line of
high-frequency electrical power output from the high-frequency
power supply device at a dummy load reproduction device that
artificially reproduces the load, and arranging, between the
high-frequency power supply device and the dummy load reproduction
device, an electrical power measuring device to be evaluated and a
reference electrical power measuring device enabling calculation of
the uncertainty of an electrical power measured value; calculating
an uncertainty range of the electrical power measured value,
according to a prescribed calculation formula, from an electrical
power measured value measured by the reference electrical power
measuring device and the uncertainty of the reference electrical
power measuring device; judging whether or not the electrical power
measured value measured by the electrical power measuring device to
be evaluated is within the uncertainty range of the electrical
power measured value of, the reference electrical power measuring
device; and evaluating the electrical power measuring device to be
evaluated as reliable if the electrical power measured value of the
electrical power measuring device to be evaluated is within the
uncertainty range of the electrical power measured value of the
reference electrical power measuring device.
2. The evaluation method according to claim 1, wherein a measured
value of forward power transmitted from the high-frequency power
supply device to the dummy load reproduction device and a measured
value of reflected power transmitted from the dummy load
reproduction device to the high-frequency power supply device are
included in the electrical power measured values of the electrical
power measuring device to be evaluated and the reference electrical
power measuring device, and wherein the reliability of the
electrical power measuring device to be evaluated is evaluated by
judging whether or not the electrical power measured value of the
electrical power measuring device to be evaluated is within the
uncertainty range of the electrical power measured value of the
reference electrical power measuring device respectively for the
forward power and the reflected power.
3. The evaluation method according to claim 1, wherein the dummy
load reproduction device has a variable reactance element, and a
plurality of complex impedances can be set by adjusting a reactance
value of the variable reactance element.
4. The evaluation method according to claim 2, wherein the dummy
load reproduction device has a variable reactance element, and a
plurality of complex impedances can be set by adjusting a reactance
value of the variable reactance element.
5. A method for evaluating the reliability of an electrical power
measuring device that is connected to a connection point between a
high-frequency power supply device and a load having a complex
impedance, the electrical power measuring device being configured
to measure the high-frequency electrical power at the connection
point, the method comprising: terminating a transmission line of
high-frequency electrical power output from the high-frequency
power supply device at a reference load having an impedance equal
to a characteristic impedance of the transmission line, arranging
an electrical power measuring device to be evaluated and a
reference electrical power measuring device enabling calculation of
the uncertainty of an electrical power measured value in the
transmission line, arranging, after the electrical power measuring
device to be evaluated and the reference electrical power measuring
device, a first impedance conversion device that converts an
impedance so that an impedance as viewed towards the reference load
side becomes the complex impedance together with arranging a first
electrical power measuring device that measures electrical power
input to the reference load between the first impedance conversion
device and the reference load, and arranging, before the electrical
power measuring device to be evaluated and the reference electrical
power measuring device, a second impedance conversion device that
converts an impedance so that an impedance as viewed towards the
reference load side becomes the characteristic impedance together
with arranging a second electrical power measuring device that
measures electrical power output from the high-frequency power
supply device between the second impedance conversion device and
the high-frequency power supply device; calculating an uncertainty
range of the electrical power measured value, according to a
prescribed calculation formula, from an electrical power measured
value measured by the reference electrical power measuring device
and the uncertainty of the reference electrical power measuring
device, and calculating a prescribed electrical power measuring
range based on an electrical power measured value measured by the
first electrical power measuring device and an electrical power
measured value measured by the second electrical power measuring
device; and evaluating the reliability of the electrical power
measuring device to be evaluated based on the electrical power
measured value measured by the electrical power measuring device to
be evaluated, the uncertainty range of the electrical power
measured value of the reference electrical power measuring device,
and the prescribed electrical power measuring range.
6. The evaluation method according to claim 5, wherein the
prescribed electrical power measuring range is a range between an
electrical power measured value of the first electrical power
measuring device and an electrical power measured value of the
second electrical power measuring device.
7. The evaluation method according to claim 5, wherein the
prescribed electrical power measuring range is a prescribed range
centered on a median value of an electrical power measured value of
the first electrical power measuring device and an electrical power
measured value of the second electrical power measuring device.
8. The evaluation method according to claim 5, wherein a judgment
is made as to whether the uncertainty range of the electrical power
measured value of the reference electrical power measuring device
is narrower than the prescribed electrical power measuring range,
in the case the uncertainty range is narrower than the prescribed
electrical power measuring range, the electrical power measuring
device to be evaluated is evaluated as being reliable if the
electrical power measured value of the electrical power measuring
device to be evaluated is within the uncertainty range of the
electrical power measured value of the reference electrical power
measuring device, and in the case the uncertainty range is not
narrower than the prescribed electrical power measuring range, the
electrical power measuring device to be evaluated is evaluated as
being reliable if a difference between a measured value of forward
power transmitted to the side of the reference load, which is the
electrical power measured value of the electrical power measuring
device to be evaluated, and a measured value of reflected power
transmitted to the side of the high-frequency power supply device,
is within the prescribed electrical power measuring range.
9. The evaluation method according to claim 1, wherein the
reference electrical power measuring device is provided with a
directional coupler, and forward power and reflected power
separated with the directional coupler are respectively
measured.
10. The evaluation method according to claim 5, wherein the
reference electrical power measuring device is provided with a
directional coupler, and forward power and reflected power
separated with the directional coupler are respectively
measured.
11. The evaluation method according to claim 9, wherein an
uncertainty range FPW of a forward power measured value and an
uncertainty range RPW of a reflected power measured value of the
reference electrical power measuring device are calculated with the
calculation formulas indicated below: FPW=Pf.times.(100-FPU)/100 to
Pf.times.(100+FPU)/100 RPW=Pr.times.(100-RPU)/100 to
Pr.times.(100+RPU)/100 where Pf: Forward power measured value Pr:
Reflected power measured value .+-.FPU: Forward power uncertainty
.+-.RPU: Reflected power uncertainty
FPU=2.times.X.times..rho.l.times.100(%)
RPU=200.times.(A+(A+C).times..rho.l+(.rho.s.times..rho.l.times..rho.l))
(%) A: Forward directivity of the directional coupler C: Reflection
coefficient of the directional coupler as viewed from the
high-frequency power supply device side .rho.s: Reflection
coefficient of the directional coupler as viewed from the load side
.rho.l: Reflection coefficient of the load as viewed from the
directional coupler.
12. The evaluation method according to claim 10, wherein an
uncertainty range FPW of a forward power measured value and an
uncertainty range RPW of a reflected power measured value of the
reference electrical power measuring device are calculated with the
calculation formulas indicated below: FPW=Pf.times.(100-FPU)/100 to
Pf.times.(100+FPU)/100 RPW=Pr.times.(100-RPU)/100 to
Pr.times.(100+RPU)/100 where Pf: Forward power measured value Pr:
Reflected power measured value .+-.FPU: Forward power uncertainty
.+-.RPU: Reflected power uncertainty
FPU=2.times.X.times..rho.l.times.100(%)
RPU=200.times.(A+(A+C).times..rho.l+(.rho.s.times..rho.l.times..rho.l))
(%) A: Forward directivity of the directional coupler C: Reflection
coefficient of the directional coupler as viewed from the
high-frequency power supply device side .rho.s: Reflection
coefficient of the directional coupler as viewed from the load side
.rho.l: Reflection coefficient of the load as viewed from the
directional coupler.
13. The evaluation method according to claim 1, wherein the
electrical power measuring device to be evaluated is a
high-frequency measuring device that measures a high-frequency
voltage and a high-frequency current, and calculates at least one
of a phase difference between the high-frequency voltage and the
high-frequency current, an impedance, a reflection coefficient,
forward power and reflected power from these measured values.
14. The evaluation method according to claim 5, wherein the
electrical power measuring device to be evaluated is a
high-frequency measuring device that measures a high-frequency
voltage and a high-frequency current, and calculates at least one
of a phase difference between the high-frequency voltage and the
high-frequency current, an impedance, a reflection coefficient,
forward power and reflected power from these measured values.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for evaluating the
reliability of electrical power measuring devices.
[0003] 2. Description of the Related Art
[0004] In the past, plasma processing systems have been developed
that process articles such as semiconductor wafers or liquid
crystal substrates using a method such as etching by supplying
high-frequency electrical power output from a high-frequency power
supply device to a plasma processing device. In these plasma
processing systems, since there is the risk of fluctuations in an
impedance of the plasma processing device causing a reflected power
reflected at the input end of the plasma processing device to
damage the high-frequency power supply device, an impedance
matching device is typically provided between the high-frequency
power supply device and the plasma processing device, and the
matching operation of the impedance matching device is controlled
corresponding to fluctuations in the impedance of the plasma
processing device, or the impedance of the plasma processing device
or high-frequency voltage and high-frequency current and the like
at the input end of the plasma processing device is monitored (see
Japanese Patent Application Laid-open No. 2007-163308).
[0005] Monitoring the matching operation of the impedance matching
device or the plasma processing device is carried out by providing
a high-frequency measuring device on the output end of the
impedance matching device and the input end of the plasma
processing device, detecting high-frequency voltage (to be simply
referred to as "voltage") and high-frequency current (to be simply
referred to as "current") with the high-frequency measuring device,
and in addition to determining a phase difference between the
voltage and current (to be simply referred to as "phase
difference") .theta. from the detected values, calculating
high-frequency parameters such as an effective voltage value V, an
effective current value I, an impedance Z=R+jX of the plasma
processing device, a reflection coefficient .GAMMA., a forward
power Pf input to the plasma processing device, and a reflected
power Pr reflected at the input end of the plasma processing device
due to impedance mismatch, and then using those high-frequency
parameters.
[0006] The high-frequency measuring device is provided with a
capacitor capacitatively coupled to a rod-shaped semiconductor for
transmitting electrical power to the plasma processing device and a
coil magnetically coupled to the body portion thereof, and together
with detecting a voltage v= {square root over (2)}Vsin(.omega.t)
with the capacitor or a current i= {square root over
(2)}Isin(.omega.t+.theta.) with the coil, a phase difference
.theta. is determined from these detected values, and the
high-frequency parameters are calculated according to equations (1)
to (5) below using the voltage v, the current i and the phase
difference .theta.. Namely, the high-frequency measuring device is
referred to as a so-called RF sensor provided with sensors for
detecting voltage v and current i, and an arithmetic processing
circuit for calculating the high-frequency parameters from the
detected values of those sensors.
R = V I cos .theta. ( 1 ) X = V I sin .theta. ( 2 ) Z = R + jX
.GAMMA. = ( R 2 + X 2 - 1 ( R + 1 ) 2 + X 2 ) 2 + ( 2 X ( R + 1 ) 2
+ X 2 ) 2 ( 3 ) Pf = VI cos .theta. 1 - .GAMMA. 2 ( 4 ) Pr = Pf
.GAMMA. 2 ( 5 ) ##EQU00001##
[0007] Since values detected with sensors differ from the correct
values due to variations in sensor sensitivity, monitoring devices
and measuring devices are typically composed to acquire calibration
data that converts detected values to correct values by
preliminarily measuring a measured object serving as a reference,
and then correcting detected values to correct detection values
with the calibration data during actual measurement.
[0008] In the case of calibrating high-frequency measuring devices,
for example, a high-frequency measuring device is arranged between
a dummy load serving as a reference measured object having a
characteristic impedance of the measuring system (a characteristic
impedance of the transmission line over which high-frequency waves
are transmitted for measurement; normally 50.OMEGA. or 75.OMEGA.)
and a high-frequency power supply device, and calibration data is
acquired for detected voltage values and detected current values of
the high-frequency measuring device when a prescribed
high-frequency electrical power is supplied from the high-frequency
power supply device to the dummy load.
[0009] However, in a plasma processing system, since the load to
which high-frequency electrical power is supplied from the
high-frequency power supply device is plasma generated within a
plasma processing device, that impedance is frequently a complex
impedance having strong reactance. Although high-frequency
electrical power PL actually input to the plasma processing device
(to be referred to as "effective power PL") is represented as
PL=Pf-Pr, as is clear from the above-mentioned equations (4) and
(5), the effective power PL is calculated by PL=VIcos .theta..
According to this equation, it is difficult to correctly calculate
the effective power PL supplied to a load having a complex
impedance unless the effective voltage value V, the effective
current value I and the phase difference .theta. are each
calculated correctly. In particular, in a plasma processing system
having for the load a plasma processing device in which the load
impedance has a phase difference .theta. close to 90.degree.
resulting in a complex impedance having large reflection, since the
error in the effective power PL becomes extremely large even if
there is only a slight error in the phase difference .theta., it is
difficult to measure effective power PL with high reliability in
high-frequency measuring devices.
[0010] In a system in which high-frequency electrical power is
supplied from a high-frequency power supply device to a load having
a complex impedance with extremely large reflection in the manner
of a plasma processing system, when the reliability of a measured
value of effective power PL supplied to the load by a
high-frequency measuring device is attempted to be evaluated,
although it is necessary to employ a method in which, for example,
a measured value is set for effective power PL that serves as a
reference when a prescribed high-frequency electrical power is
supplied to a load having a complex impedance, and a measured value
of the effective power PL of the high-frequency measuring device is
evaluated by comparing with the reference measured value, such a
method for evaluating the reliability of an electrical power
measured value of a high-frequency measuring device has yet to be
proposed.
[0011] Consequently, there has previously been the problem of being
unable to evaluate the reliability of high-frequency measuring
devices for measuring the effective power input to a load having a
complex impedance. In addition, since criteria for evaluating
reliability during manufacturing of high-frequency measuring
devices are not clearly defined, it was also difficult to inspect
for defective products.
SUMMARY OF THE INVENTION
[0012] With the foregoing in view, an object of the present
invention is to provide a method for evaluating the reliability of
an electrical power measuring device used for a load other than
that having a characteristic impedance.
[0013] The present invention devises the following technical means
for solving the above-mentioned problems.
[0014] A method for evaluating the reliability of electrical power
measuring devices provided according to a first aspect of the
present invention is a method for evaluating, using a prescribed
evaluation system, the reliability of an electrical power measuring
device that is connected to a connection point between a
high-frequency power supply device and a load having a complex
impedance to which high-frequency electrical power is supplied from
the high-frequency power supply device, and measures the
high-frequency electrical power at the connection point. The
evaluation system is configured by terminating a transmission line
of high-frequency electrical power output from the high-frequency
power supply device at a dummy load reproduction device that
artificially reproduces the load, and arranging an electrical power
measuring device to be evaluated and a reference electrical power
measuring device enabling calculation of the uncertainty of an
electrical power measured value between the high-frequency power
supply device and the dummy load reproduction device. An
uncertainty range of the electrical power measured value is
calculated according to a prescribed calculation formula from an
electrical power measured value measured by the reference
electrical power measuring device and the uncertainty of the
reference electrical power measuring device. A judgment is made as
to whether or not the electrical power measured value measured by
the electrical power measuring device to be evaluated is within the
uncertainty range of the electrical power measured value of the
reference electrical power measuring device, and the electrical
power measuring device to be evaluated is evaluated as being
reliable if the electrical power measured value of the electrical
power measuring device to be evaluated is within the uncertainty
range of the electrical power measured value of the reference
electrical power measuring device.
[0015] Furthermore, the term "uncertainty" refers to a parameter
that characterizes the variation of a value able to be logically
correlated with a measured quantity incidental to a measurement
result, and indicates to what degree of range of variation from a
measured value a "true value" is present. In addition, the range
over which this "true value" is able to be present is referred to
as the "uncertainty range".
[0016] In a preferred embodiment of the present invention, a
measured value of forward power transmitted from the high-frequency
power supply device to the dummy load reproduction device and a
measured value of reflected power transmitted from the dummy load
reproduction device to the high-frequency power supply device are
included in the electrical power measured values of the electrical
power measuring device to be evaluated and the reference electrical
power measuring device, and the reliability of the electrical power
measuring device to be evaluated is evaluated by judging whether or
not the electrical power measured value of the electrical power
measuring device to be evaluated is within the uncertainty range of
the electrical power measured value of the reference electrical
power measuring device respectively for the forward power and
reflected power.
[0017] In a preferred embodiment of the present invention, the
dummy load reproduction device has a variable reactance element,
and a plurality of complex impedances can be set by adjusting a
reactance value of the variable reactance element.
[0018] A method for evaluating the reliability of electrical power
measuring devices provided according to a second aspect of the
present invention is a method for evaluating, using a prescribed
evaluation system, the reliability of an electrical power measuring
device that is connected to a connection point between a
high-frequency power supply device and a load having a complex
impedance to which high-frequency electrical power is supplied from
the high-frequency power supply device, and measures the
high-frequency electrical power at the connection point. The
evaluation system is configured by terminating a transmission line
of high-frequency electrical power output from the high-frequency
power supply device at a reference load having an impedance equal
to a characteristic impedance of the transmission line, arranging
an electrical power measuring device to be evaluated and a
reference electrical power measuring device enabling calculation of
the uncertainty of an electrical power measured value in the
transmission line, arranging, after the electrical power measuring
device to be evaluated and the reference electrical power measuring
device, a first impedance conversion device that converts an
impedance so that an impedance as viewed towards the reference load
side becomes a complex impedance together with arranging a first
electrical power measuring device that measures electrical power
input to the reference load between the first impedance conversion
device and the reference load, and arranging, before the electrical
power measuring device to be evaluated and the reference electrical
power measuring device, a second impedance conversion device that
converts an impedance so that an impedance as viewed towards the
reference load side becomes a characteristic impedance together
with arranging a second electrical power measuring device that
measures electrical power output from the high-frequency power
supply device between the second impedance conversion device and
the high-frequency power supply device. An uncertainty range of the
electrical power measured value is calculated according to a
prescribed calculation formula from an electrical power measured
value measured by the reference electrical power measuring device
and the uncertainty of the reference electrical power measuring
device, and a prescribed electrical power measuring range is
calculated based on an electrical power measured value measured by
the first electrical power measuring device and an electrical power
measured value measured by the second electrical power measuring
device, and the reliability of the electrical power measuring
device to be evaluated is evaluated based on the electrical power
measured value measured by the electrical power measuring device to
be evaluated, the uncertainty range of the electrical power
measured value of the reference electrical power measuring device,
and the prescribed electrical power measuring range.
[0019] In a preferred embodiment of the present invention, the
prescribed electrical power measuring range is a range between an
electrical power measured value of the first electrical power
measuring device and an electrical power measured value of the
second electrical power measuring device.
[0020] In a preferred embodiment of the present invention, the
prescribed electrical power measuring range is a prescribed range
centered on a median value of an electrical power measured value of
the first electrical power measuring device and an electrical power
measured value of the second electrical power measuring device.
[0021] In a preferred embodiment of the present invention, a
judgment is made as to whether the uncertainty range of the
electrical power measured value of the reference electrical power
measuring device is narrower than the prescribed electrical power
measuring range, and in the case the uncertainty range is narrower
than the prescribed electrical power measuring range, the
electrical power measuring device to be evaluated is evaluated as
being reliable if the electrical power measured value of the
electrical power measuring device to be evaluated is within the
uncertainty range of the electrical power measured value of, the
reference electrical power measuring device, while in the case the
uncertainty range is not narrower than the prescribed electrical
power measuring range, the electrical power measuring device to be
evaluated is evaluated as being reliable if a difference between a
measured value of forward power transmitted to the side of the
reference load, which is the electrical power measured value of the
electrical power measuring device to be evaluated, and a measured
value of reflected power transmitted to the side of the
high-frequency power supply device, is within the prescribed
electrical power measuring range.
[0022] In a preferred embodiment of the present invention, the
reference electrical power measuring device is provided with a
directional coupler, and forward power and reflected power
separated with the directional coupler are respectively
measured.
[0023] In a preferred embodiment of the present invention, an
uncertainty range FPW of a forward power measured value and an
uncertainty range RPW of a reflected power measured value of the
reference electrical power measuring device are calculated with the
calculation formulas indicated below:
FPW=Pf.times.(100-FPU)/100 to Pf.times.(100+FPU)/100
RPW=Pr.times.(100-RPU)/100 to Pr.times.(100+RPU)/100
where
[0024] Pf: Forward power measured value
[0025] Pr: Reflected power measured value
[0026] .+-.FPU: Forward power uncertainty
[0027] .+-.RPU: Reflected power uncertainty
[0028] FPU=2.times.C.times..rho.l.times.100(%)
[0029]
RPU=200.times.(A+(A+C).times..rho.l+(.rho.s.times..rho.l.times..rho-
.l)) (%)
[0030] A: Forward directivity of the directional coupler
[0031] C: Reflection coefficient of the directional coupler as
viewed from the high-frequency power supply device side
[0032] .rho.s: Reflection coefficient of the directional coupler as
viewed from the load side
[0033] .rho.l: Reflection coefficient of the load as viewed from
the directional coupler
[0034] Furthermore, "reflection coefficients" are more precisely
represented by the magnitude (absolute value) and phase thereof,
and are described as "reflection coefficients" even in the case of
referring only the magnitude of thereof. The reflection
coefficients C, .rho.s and .rho.l represent the magnitude of those
reflection coefficients. In addition, directivity A represents the
magnitude of directivity.
[0035] In a preferred embodiment of the present invention, the
electrical power measuring device to be evaluated is a
high-frequency measuring device that measures a high-frequency
voltage and a high-frequency current, and calculates at least one
of a phase difference between the high-frequency voltage and the
high-frequency current, an impedance, a reflection coefficient,
forward power and reflected power from these measured values.
[0036] According to the present invention, high-frequency
electrical power supplied from a high-frequency power supply device
to a dummy load having a complex impedance (that includes a forward
power and a reflected power) is respectively measured by an
electrical power measuring device to be evaluated and a reference
electrical power measuring device. In the reference electrical
power measuring device, an uncertainty range of an electrical power
measured value is calculated according to a prescribed calculation
formula from the electrical power measured value. Since the
electrical power measuring device to be evaluated and the reference
electrical power measuring device measure high-frequency electrical
power transmitted along the same transmission line, if an
electrical power measured value of the electrical power measuring
device to be evaluated is within the uncertainty range of an
electrical power measured value of the reference electrical power
measuring device, then the electrical power measured value of the
electrical power measuring device to be evaluated can be judged to
be reliable, and the electrical power measuring device to be
evaluated can be evaluated as being reliable.
[0037] Namely, if an electrical power measured value of the
electrical power measuring device to be evaluated is defined as
"Pf1", an electrical power measured value of the reference
electrical power measuring device is defined as "Pf2", and the
uncertainty range of the electrical power measured value Pf2 is
defined as "Pf2.+-..DELTA.Uf", the electrical power measuring
device to be evaluated is evaluated as being reliable if
Pf2-.DELTA.Uf.ltoreq.Pf1.ltoreq.Pf2+.DELTA.Uf.
[0038] As a result, an electrical power measured value measured by
an electrical power measuring device evaluated as being reliable
can be guaranteed to be reliable. In addition, inspections for
defective products can be preferably carried out by evaluating the
reliability of an electrical power measuring device during
manufacturing of that electrical power measuring device.
[0039] In addition, according to the present invention, a first
impedance conversion device, which converts a reference load to a
complex impedance, and a second impedance conversion device, which
further converts the complex impedance to a characteristic
impedance, are provided on a transmission line in which
high-frequency electrical power is supplied from a high-frequency
power supply device to a reference load having an impedance equal
to the characteristic impedance, and high-frequency electrical
power (including forward power, reflected power and differential
electrical power between the forward power and the reflected power)
is respectively measured by an electrical power measuring device to
be evaluated and a reference electrical power measuring device on
the transmission line between the first and second impedance
conversion devices. In addition, high-frequency electrical power
(forward power) input to the reference load is measured by a first
electrical power measuring device between the reference load and
the first impedance conversion device, and high-frequency
electrical power (reflected power) output from the high-frequency
power supply device is measured by a second electrical power
measuring device between the high-frequency power supply device and
the second impedance conversion device.
[0040] An uncertainty range of a measured value of high-frequency
electrical power is calculated according to a prescribed
calculation formula from a measured value of high-frequency
electrical power of a reference electrical power measuring device
and the uncertainty of the reference electrical power measuring
device. In addition, a prescribed electrical power measuring range
is calculated based on a measured value of high-frequency
electrical power of the first electrical power measuring device and
a measured value of high-frequency electrical power of the second
electrical power measuring device.
[0041] In the case the uncertainty range of the measured value of
high-frequency electrical power of the reference electrical power
measuring device is narrower than the prescribed electrical power
measuring range, an electrical power measuring device to be
evaluated is evaluated as being reliable if an electrical power
measured value of the electrical power measuring device to be
evaluated is within the uncertainty range of the electrical power
measured value of the reference electrical power measuring device.
On the other hand, in the case the uncertainty range of a measured
value of high-frequency electrical power of the reference
electrical power measuring device is not narrower than the
prescribed electrical power measuring range, the electrical power
measuring device to be evaluated is evaluated as being reliable if
the difference between a measured value of forward power and a
measured value of reflected power of the electrical power measuring
device to be evaluated is within the prescribed electrical power
measuring range.
[0042] Namely, if measured values of forward power and reflected
power of the electrical power measuring device to be evaluated are
defined as "Pf1" and "Pr1", the prescribed electrical power
measuring range is defined as "Pf3 to Pf4" (<Pf3), measured
values of forward power and reflected power of the reference
electrical power measuring device are defined as "Pf2" and "Pr2",
the uncertainty range of the measured value Pf2 of forward power is
defined as "Pf2.+-..DELTA.Uf", and the uncertainty range of the
measured value Pr2 of reflected power is defined as
"Pr2.+-..DELTA.Ur", in the case of
2(.DELTA.Uf+.DELTA.Ur)<(Pf3-Pf4), the electrical power measuring
device to be evaluated is evaluated as being reliable if
Pf2-.DELTA.Uf.ltoreq.Pf1.ltoreq.Pf2+.DELTA.Uf, while in the case of
2(.DELTA.Uf+.DELTA.Ur).gtoreq.(Pf4-Pf3), the electrical power
measuring device to be evaluated is evaluated as being reliable if
Pf4<(Pf1-Pr1)<Pf3.
[0043] Thus, since the reliability of an electrical power measuring
device to be evaluated is evaluated under stricter conditions, the
reliability of the electrical power measuring device to be
evaluated can be evaluated more severely.
[0044] Other characteristics and advantages of the present
invention will become clearer from the detailed explanation
provided below with reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a drawing for explaining the concept of a first
embodiment of the evaluation method according to the present
invention;
[0046] FIG. 2 is a drawing showing an example of an evaluation
system for carrying out a first embodiment of the evaluation method
according to the present invention;
[0047] FIG. 3 consists of circuit diagrams showing examples of a
variable load device;
[0048] FIG. 4 is a drawing showing an example of the configuration
of a reference electrical power measuring device;
[0049] FIG. 5 is a drawing showing an example of the configuration
of a high-frequency measuring device;
[0050] FIG. 6 is a flow chart for explaining the procedure of an
evaluation method according to a first embodiment;
[0051] FIG. 7 is a drawing showing an example of an evaluation
system for carrying out a second embodiment of the evaluation
method according to the present invention; and
[0052] FIG. 8 is a flow chart for explaining the procedure of an
evaluation method according to a second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] The following provides a detailed explanation of embodiments
of the present invention with reference to the appended
drawings.
[0054] FIG. 1 is a drawing for explaining the concept of a first
embodiment of a method for evaluating measurement accuracy of a
high-frequency measuring device according to the present
invention.
[0055] An electrical power measuring system for evaluating
electrical power measurement accuracy of a high-frequency measuring
device employs a configuration in which a transmission line of
high-frequency electrical power output from a high-frequency power
supply E is terminated at a termination resistor Ro having a
characteristic impedance (for example, 50.OMEGA.) of an electrical
power measuring system, high-frequency measuring device X to be
evaluated and a high-frequency electrical power measuring device
serving as an evaluation reference capable of calculating the
uncertainty of a measured value (to be referred to as a "reference
electrical power measuring device") Y are arranged in series at an
intermediate location of the transmission line, and together with
arranging an impedance conversion device B1 between the
high-frequency measuring device X and the termination resistor Ro,
an impedance conversion device B2 is arranged between the reference
electrical power measuring device Y and the high-frequency power
supply E. Furthermore, the high-frequency measuring device X
fulfills the same function as an RF sensor explained in the prior
art.
[0056] The impedance conversion device B1 is for converting an
impedance of the termination resistor Ro so that an impedance
viewed from the output end d of the high-frequency measuring device
X towards the load side becomes a desired complex impedance
ZL=R+jX. In addition, the impedance conversion device B2 is for
converting the impedance ZL=R'+jX' as viewed from the input end b
of the reference electrical power measuring device Y towards the
load side so that an impedance as viewed from the output end a of
the high-frequency power supply E towards the load side becomes a
characteristic impedance Ro.
[0057] Furthermore, since the input and output impedances of the
high-frequency measuring device X and the reference electrical
power measuring device Y are designed to be the characteristic
impedance Ro, an impedance of the electrical power measuring system
shown in FIG. 1 is laterally symmetrical about a central point c.
Thus, in the case of configuring such that the input and output
sides of the impedance conversion device B2 on the side of the
high-frequency power supply E are inversely connected in the same
circuit as the impedance conversion device B1 on the load side, an
impedance as viewed from the output end b of the impedance
conversion device B2 towards the power supply side is equal to the
complex impedance ZL=R+jX as viewed from the input end d of the
impedance conversion device B1 towards the load side.
[0058] The basis of the evaluation method according to a first
embodiment consists of respectively measuring forward power and
reflected power flowing through a transmission line on a
transmission line having a complex impedance ZL positioned between
both ends thereof with the high-frequency measuring device X and
the reference electrical power measuring device Y, calculating
uncertainty ranges Pf2.+-..DELTA.Uf (provided that,
.DELTA.Uf=Pf2FPU/100) and Pr2.+-..DELTA.Ur (provided that,
.DELTA.Ur=Pr2RPU/100) of forward power measured value Pf2 and
reflected power measured value Pr2 of the reference electrical
power measuring device Y from the forward power Pf2 and the
reflected power Pr2 and their respective uncertainties .+-.FPU(%)
and .+-.RPU(%), and respectively comparing the forward power
measured value Pf1 and the reflected power measured value Pr1
measured with the high-frequency measuring device X with the
uncertainty range Pf2.+-..DELTA.Uf of the forward power measured
value Pf2 and the uncertainty range Pr2.+-..DELTA.Ur of the
reflected power measured value Pr2, and if the forward power Pf1 is
within the uncertainty range Pf2.+-..DELTA.Uf and the reflected
power Pr1 is within the uncertainty range Pr2.+-..DELTA.Ur, then
the forward power measured value Pf1 and the reflected power
measured value Pr1 of the high-frequency measuring device X can be
judged to be reliable, and the high-frequency measuring device X
can be evaluated as being reliable.
[0059] Namely, when the reference electrical power measuring device
Y, for which uncertainty of electrical power measured values is
clear, is used as a reference, if an electrical power measured
value of the high-frequency measuring device X measured under
identical conditions is within the uncertainty range of electrical
power measured values of the reference electrical power measuring
device Y, then the high-frequency measuring device X is evaluated
as being reliable.
[0060] Furthermore, in the case the uncertainty range of electrical
power measured values of the reference electrical power measuring
device Y is broad, the reliability of the high-frequency measuring
devices X becomes low even if an electrical power measured value of
the high-frequency measuring device X is within the uncertainty
range of electrical power measured values of the reference
electrical power measuring device Y. Thus, in the evaluation method
according to the first embodiment, an electrical power Pf3 and Pf4
are respectively measured at the output end a of the high-frequency
power supply E and an input end e of the termination resistor Ro,
and in the case the range Pf3 to Pf4 (>Pf3) of both electrical
power measured values is narrower than the uncertainty range of
electrical power measured values of the reference electrical power
measuring device Y, reliability of the high-frequency measuring
device X is evaluated based on the range Pf3 to Pf4 of the
electrical power measured values as described below.
[0061] Namely, since impedance matching is obtained at the output
end a of the high-frequency power supply E, the detected electrical
power Pf3 at the output end a can be considered to essentially be
forward power, and the detected electrical power Pf3 is equivalent
to a difference PL between forward power and reflected power at an
output end c of the of the reference electrical power measuring
device Y. On the other hand, although the difference PL is the
electrical power input to the termination resistor Ro, since
impedance matching is obtained at the input end e of the
termination resistor Ro, detected electrical power Pf4 at the input
end e can be considered to essentially be forward power, and the
difference PL is equivalent to the detected electrical power Pf4.
Since the impedance conversion devices B1 and B2 have extremely low
power loss, Pf4<PL<Pf3 ought to theoretically be valid. Thus,
if the difference (Pf1-Pr1) between the forward power Pf1 and the
reflected power Pr1 measured with the high-frequency measuring
device X is within the range of Pf4<(Pf1-Pr1)<Pf3, then the
high-frequency measuring device X can be evaluated as being
reliable.
[0062] If the inequality 2(.DELTA.Uf+.DELTA.Ur)>(Pf3-Pf4) is
valid between measured electrical power measured values Pf3 and Pf4
and the uncertainty range (Pf2-Pr2).+-.(.DELTA.Uf+.DELTA.Ur) of the
difference between forward power measured value Pf2 and reflected
power measured value Pr2 of the reference electrical power
measuring device Y, since the range Pf3 to Pf4 of both electrical
power measured values is narrower than the uncertainty range of
electrical power measured values of the reference electrical power
measuring device Y, a judgment is made as to whether or not
Pf4<(Pf1-Pr1)<Pf3 is valid. At this time, if
Pf4<(Pf1-Pr1)<Pf3 is valid, then the high-frequency measuring
device X is evaluated as being reliable.
[0063] Thus, in the evaluation method according to the first
embodiment, the uncertainty range
(Pf2-Pr2).+-.(.DELTA.Uf+.DELTA.Ur) of the difference between
measured values Pf2 and Pr2 of forward power and reflected power of
the reference electrical power measuring device Y is calculated
using the measured values Pf2 and Pr2 and known uncertainties
.+-.FPU(%) and .+-.RPU(%), and a judgment is made as which of the
difference uncertainty range (Pf2-Pr2).+-.(.DELTA.Uf+.DELTA.Ur) or
the range Pf3 to Pf4 of both electrical power measured values at
the input end a and the output end e is narrower. In the case the
difference uncertainty range (Pf2-Pr2) (.DELTA.Uf+.DELTA.Ur) is
narrower, reliability is evaluated by comparing the forward power
measured value Pf1 of the high-frequency measuring device X with
the uncertainty range Pf2.+-..DELTA.Uf and comparing the reflected
power measured value Pr1 with the uncertainty range
Pr2.+-..DELTA.Ur, while in the case the range Pf3 to Pf4 of both
electrical power measured values is narrower, reliability is
evaluated by comparing the difference (Pf1-Pr1) between the forward
power measured value Pf1 and the reflected power measured value Pr1
of the high-frequency measuring device X with the electrical power
measuring range Pf3 to Pf4.
[0064] Next, an explanation is provided of an evaluation system for
evaluating the reliability of a high-frequency measuring device
using the evaluation method according to the first embodiment.
[0065] FIG. 2 is a drawing showing the configuration of an
evaluation system for carrying out the evaluation method according
to the first embodiment.
[0066] As shown in this drawing, an evaluation system A is provided
with a high-frequency power supply device 1, a power meter 2, an
impedance conversion device 3, a reference electrical power
measuring device 4, a high-frequency measuring device 5, an
impedance conversion device 6, a power meter 7, a reference load 8
and a control device 9. The evaluation system A evaluates the
reliability of the high-frequency measuring device 5, evaluates the
high-frequency measuring device 5 as being reliable in the case an
electrical power measured value of the high-frequency measuring
device 5 is within a prescribed range, or evaluates the
high-frequency measuring device 5 as being unreliable in the case
an electrical power measured value of the high-frequency measuring
device 5 is outside the prescribed range. The high-frequency power
supply device 1, the power meter 2, the impedance conversion device
3, the reference electrical power measuring device 4, the
high-frequency measuring device 5, the impedance conversion device
6, the power meter 7 and the reference load 8 are respectively
connected on a transmission line composed of, for example, a
coaxial cable in that order. Furthermore, the arrangement of the
reference electrical power measuring device 4 and the
high-frequency measuring device 5 may be inverted. In addition, the
evaluation system A is configured as an electrical power measuring
system having a characteristic impedance of 50 .OMEGA..
[0067] The high-frequency power supply device 1 supplies
high-frequency electrical power, and is a power supply device
capable of outputting high-frequency electrical power having a
frequency of, for example, several hundred kHz or more. A
high-frequency power supply device similar to that typically used
in plasma processing of a plasma processing device is used for the
high-frequency power supply device 1.
[0068] The power meter 2 measures forward power from the
high-frequency power supply device 1 and reflected power from the
impedance conversion device 3 at the output end a of the
high-frequency power supply device 1. The forward power Pf3 and the
reflected power Pr3 measured by the power meter 2 are input to the
control device 9. The power meter 7 measures forward power from the
impedance conversion device 6 and reflected power from the
reference load 8 at the input end e of the reference load 8. The
forward power Pf4 and the reflected power Pr4 measured by the power
meter 7 are input to the control device 9. In the present
embodiment, the power meter 2 and the power meter 7 are electrical
power measuring devices that use directional couplers, and are
configured in the same manner as the reference electrical power
measuring device 4 to be subsequently described. Furthermore, since
the power meter 2 and the power meter 7 measure the forward power
Pf3 and Pf4 when the reflected power Pr3 and Pr4 are at zero, even
if the directivity of the directional couplers is not as high as
the reference electrical power measuring device 4, the measurement
accuracy of the measured forward power Pf3 and Pf4 is sufficiently
high (for example, within .+-.1%). Furthermore, the power meter 2
and the power meter 7 are suitably calibrated, and the electrical
power measured values output thereby are output as correct values.
Furthermore, the power meter 2 and the power meter 7 are not
limited thereto, but rather may be any electrical power measuring
device that measures forward power and reflected power.
[0069] When the reflected power Pr3 and the reflected power Pr4 are
at zero, electrical power output by the high-frequency power supply
device 1 is input to the impedance conversion device 3 without
being reflected, and electrical power output by the impedance
conversion device 6 is input to the reference load 8 without being
reflected. At this time, the forward power Pf3 measured by the
power meter 2 and the forward power Pf4 measured by the power meter
7 are measured with sufficiently high accuracy. In addition, as was
previously described, the difference PL between forward power and
reflected power measured at a location between the output end b and
the input end d ought to be between the forward power Pf3 measured
by the power meter 2 and the forward power Pf4 measured by the
power meter 7. In the present embodiment, the reliability of the
high-frequency measuring device 5 is evaluated according to whether
or not the difference (Pf1-Pr1) between the forward power Pf1 and
reflected power Pr1 measured with the high-frequency measuring
device 5 is within the range between the forward power Pf3 and the
forward power Pf4.
[0070] The impedance conversion devices 3 and 6 are for converting
an impedance. The impedance conversion device 6 is for reproducing
the actual complex impedance generated in the plasma processing
device used by the high-frequency measuring device 5, and converts
an impedance of the reference load 8 so that an impedance viewed
from the input end c of the high-frequency measuring device 5
towards the side of the reference load 8 becomes a desired complex
impedance. Since the actual complex impedance generated in the
plasma processing device changes over a fixed range, a variable
reactance element is contained in the impedance conversion device 6
so as to be able to reproduce a plurality of representative values
of that range of change, and a plurality of representative values
(complex impedances) are reproduced by changing the variable
reactance element.
[0071] FIG. 3(b) is a circuit diagram showing an example of the
impedance conversion device 6.
[0072] As shown in FIG. 3(b), the impedance conversion device 6 has
an inductor L2 and variable reactance elements in the form of
variable capacitors VC3 and VC4 connected in an L configuration.
The capacitances C3 and C4 of the variable capacitors VC3 and VC4
can be changed in a stepwise manner. The impedance conversion
device 6 converts an impedance of the reference load 8 so that an
impedance viewed from the input end c of the high-frequency
measuring device 5 towards the side of the reference load 8 becomes
a desired complex impedance by changing the capacitances C3 and C4
to vary the impedance.
[0073] Adjustment values of the capacitances C3 and C4 for
reproducing a plurality of complex impedances are preset in the
following manner using an impedance analyzer. First, the portion of
the evaluation system A shown in FIG. 2 from the high-frequency
power supply device 1 to the reference electrical power measuring
device 4 is removed, and the impedance analyzer is connected to the
input end c of the high-frequency measuring device 5. The
capacitances C3 and C4 of the variable capacitors VC3 and VC4 are
then changed while monitoring the measured values of the impedance
analyzer. Adjustment positions of the variable capacitors VC3 and
VC4 (values of the capacitances C3 and C4) are acquired when the
measured value of the impedance analyzer becomes a desired complex
impedance, and set for the impedance conversion device 6. As a
result, the impedance conversion device 6 is able to reproduce a
desired complex impedance.
[0074] The impedance conversion device 3 matches a complex
impedance converted with the impedance conversion device 6 to the
high-frequency power supply device 1, and converts an impedance
viewed from the input end b of the reference electrical power
measuring device 4 towards the load side so that an impedance
viewed from the output end a of the high-frequency power supply
device 1 towards the side of the reference load 8 becomes a
characteristic impedance. A variable reactance element is contained
in the impedance conversion device 3, and an impedance viewed from
the output end a of the high-frequency power supply device 1
towards the side of the reference load 8 is converted to a
characteristic impedance by changing the variable reactance
element.
[0075] FIG. 3(a) is a circuit diagram showing an example of the
impedance conversion device 3.
[0076] As shown in FIG. 3(a), the impedance conversion device 3 has
an inductor L1 and variable reactance elements in the form of
variable capacitors VC1 and VC2 connected in an L configuration.
The capacitances C1 and C2 of the variable capacitors VC1 and VC2
can be changed in a stepwise manner. The impedance conversion
device 3 converts an impedance viewed from the output end a of the
high-frequency power supply device 1 towards the side of the
reference load 8 to a characteristic impedance by changing the
capacitances C1 and C2 to vary the impedance.
[0077] The inductor L1, variable capacitor VC1 and variable
capacitor VC2 of the impedance conversion device 3 respectively use
elements in common with the inductor L2, variable capacitor VC3 and
variable capacitor VC4 of the impedance conversion device 6. In
addition, as shown in the drawing, in the impedance conversion
device 3, in contrast to the inductor L1 and the variable capacitor
VC1 being connected in series in that order from the input side and
the variable capacitor VC2 being connected in parallel there from
to the output side, in the impedance, conversion device 6, the
inductor L2 and the variable capacitor VC3 are connected in series
in that order from the output side and the variable capacitor VC4
is connected in parallel there from to the input side. Namely, the
impedance conversion device 6 can be considered as having
interchanged the input side and output side from that of the
impedance conversion device 3. As a result, if the capacitance C1
of the variable capacitor VC1 and the capacitance C2 of the
variable capacitor VC2 are respectively made to coincide with the
capacitance C3 of the variable capacitor VC3 and the capacitance C4
of the variable capacitor VC4, an impedance viewed from the output
end a of the high-frequency power supply device 1 towards the side
of the reference load 8 can theoretically be matched to a
characteristic impedance that is the impedance of the reference
load 8. Furthermore, since there is actually variation between
elements, the impedance is not made to completely match, but rather
serves as a reference for adjustment.
[0078] Furthermore, the configuration of the impedance conversion
devices 3 and 6 is not limited thereto, but is only required to be
that which enables conversion of an impedance. For example, the
variable reactance element may be in the form of variable
inductance. In addition, when not considering the bother of
adjustment, the arrangement of elements of the impedance conversion
device 3 and the arrangement of elements of the impedance
conversion device 6 are not required to be mutually
symmetrical.
[0079] The reference electrical power measuring device 4 measures
forward power from the impedance conversion device 3 and reflected
power of the impedance conversion device 6 at the input end c of
the high-frequency measuring device 5. The forward power Pf2 and
the reflected power Pr2 measured by the reference electrical power
measuring device 4 are input to the control device 9.
[0080] FIG. 4 is a drawing showing an example of the configuration
of the reference electrical power measuring device 4.
[0081] As shown in the drawing, the reference electrical power
measuring device 4 is provided with a directional coupler 41, a
power meter 42 and a power meter 43. The directional coupler 41
separates electrical power into a forward wave and a reflected wave
and outputs each wave. The power meter 42 is a terminated power
meter that measures and outputs forward power Pf2 from the forward
wave input by the directional coupler 41. The power meter 43 is
also a terminated power meter, and measures and outputs reflected
power Pr2 from the reflected wave input from the directional
coupler 41. Furthermore, the power meter 42 and the power meter 43
are suitably calibrated, and electrical power measured values
output thereby are output as correct values. Furthermore, the
above-mentioned power gauges 2 and 7 also have a similar
configuration to those of the reference electrical power measuring
device 4.
[0082] Since measured values measured by the reference electrical
power measuring device 4 serve as a reference for evaluating
electrical power measured values of the high-frequency measuring
device 5, it is necessary to use a device having high measurement
accuracy for the reference electrical power measuring device 4. In
the present embodiment, a direction coupler having high directivity
(for example, about -50 dB) is used for the directional coupler 41
of the reference electrical power measuring device 4. Furthermore,
the configuration of the reference electrical power measuring
device 4 is not limited thereto, but rather may be that of any
electrical power measuring device that is capable of accurately
measuring forward power and reflected power and enables calculation
of uncertainty.
[0083] In general, the uncertainty of a directional coupler is
calculated according to the following equation (6). The uncertainty
of an electrical power measuring device provided with a directional
coupler can be considered to be equal to the uncertainty of the
directional coupler. Thus, the uncertainty of the reference
electrical power measuring device 4 is calculated according to the
following equation (6) using each parameter of the directional
coupler 41:
.+-.FPU=.+-.2.times.C.times..rho.l.times.100(%)
.+-.RPU=.+-.200.times.(A+(A+C).times..rho.l+(.rho.s.times..rho.l.times..-
rho.l)) (%) (6)
[0084] .+-.FPU: Forward power uncertainty
[0085] .+-.RPU: Reflected power uncertainty
[0086] A: Forward directivity of the directional coupler
[0087] C: Reflection coefficient of the directional coupler as
viewed from the power supply
[0088] .rho.s: Reflection coefficient of the directional coupler as
viewed from the load
[0089] .rho.l: Reflection coefficient of the load as viewed from
the directional coupler
[0090] The forward directivity A of the directional coupler, the
reflection coefficient C of the directional coupler as viewed from
the power supply, and the reflection coefficient .rho.s of the
directional coupler as viewed from the load differ according to the
directional coupler used and are determined in advance. The
reflection coefficient .rho.l of the load as viewed from the
directional coupler is measured using a network analyzer when
setting a desired complex impedance for the impedance conversion
device 6.
[0091] The "true value" of measured values of an electrical power
measuring device for which uncertainty has been calculated is
within the uncertainty range calculated from the measured value and
the uncertainty. For example, in the case forward power Pf2 is
measured by the reference electrical power measuring device 4, the
"true value" can be considered to be between Pf2(100-FPU)/100 and
Pf2(100+FPU)/100. In the present embodiment, reliability of the
high-frequency measuring device 5 is evaluated based on whether or
not the forward power Pf1 and the reflected power Pr1 measured by
the high-frequency measuring device 5 are respectively within the
uncertainty ranges of forward power Pf2 and reflected power Pr2
measured by the reference electrical power measuring device 4.
Furthermore, the equation for calculating uncertainty is not
limited to the equation (6) described above.
[0092] The high-frequency measuring device 5 is an electrical power
measuring device for which reliability is evaluated by the
evaluation system A. The high-frequency measuring device 5 measures
forward power from the impedance conversion device 3 and reflected
power from the impedance conversion device 6 at the output end c of
the reference electrical power measuring device 4. The
high-frequency measuring device 5 is a so-called RF sensor that
detects voltage and current of a transmission line at the output
end c and calculates forward power Pf1 and reflected power Pr1
using the previously described equations (1) to (5). Forward power
Pf1 and reflected power Pr1 measured by the high-frequency
measuring device 5 are input to the control device 9.
[0093] FIG. 5 is a drawing showing an example of the configuration
of the high-frequency measuring device 5.
[0094] As shown in the drawing, the high-frequency measuring device
5 is provided with a current transformer unit 51, a current
conversion circuit 52, a capacitor unit 53, a voltage conversion
circuit 54 and an electrical power arithmetic processing circuit
55. The current transformer unit 51 detects current corresponding
to high-frequency current flowing to a transmission line 56, and
the detected current is output to the current conversion circuit
52. The current conversion circuit 52 converts the input current to
a current signal i of a prescribed current level and outputs that
current signal i to the electrical power arithmetic processing
circuit 55. The capacitor unit 53 detects voltage corresponding to
high-frequency voltage generated in the transmission line 56, and
outputs the detected voltage to the voltage conversion circuit 54.
The voltage conversion circuit 54 converts the input voltage to a
voltage signal v of a prescribed voltage level and outputs that
signal to the electrical power arithmetic processing circuit 55.
The electrical power arithmetic processing circuit 55 determines a
phase difference .theta. from the current signal i input from the
current conversion circuit 52 and the voltage signal v input from
the voltage conversion circuit 54, and calculates an effective
voltage value V and a an effective current value I. In addition,
the electrical power arithmetic processing circuit 55 calculates
and outputs forward power Pf1 and reflected power Pr1 using the
previously described equations (1) to (5) from the phase difference
.theta., the effective voltage value V and the effective current
value I. Furthermore, the current conversion circuit 52 and the
voltage conversion circuit 54 are suitably calibrated, and the
current signal i and the voltage signal v output thereby are output
as correct values.
[0095] The reference load 8 is a so-called reflection-free
termination, and is for terminating a transmission line of
electrical power output from the high-frequency power supply device
1 in the absence of reflection.
[0096] The control device 9 controls the evaluation system A. The
control device 9 is input with respective measured values of
forward power and reflected power from the power meter 2, the
reference electrical power measuring device 4, the high-frequency
measuring device 5 and the power meter 7, evaluates reliability of
the high-frequency measuring device 5, and displays the evaluation
result on a display unit not shown. The control unit 9 judges which
range of the i uncertainty range of the difference between forward
power Pf2 and reflected power Pr2 input from the reference
electrical power measuring device 4 and the range between forward
power Pf3 input from the power meter 2 and forward power Pf4 input
from the power meter 7 is narrower when the reflected power Pr3
input from the power meter 2 and the reflected power Pr4 input from
the power meter 7 are at zero. This is for evaluating the
reliability of the high-frequency measuring device 5 more severely
by comparing electrical power measured values of the high-frequency
measuring device 5 under stricter conditions (conditions having a
narrower range).
[0097] In the case the uncertainty range of the difference between
forward power Pf2 and reflected power Pr2 is narrower, the control
device 9 evaluates reliability of the high-frequency measuring
device 5 based on whether or not the forward power Pf1 and the
reflected power Pr1 are respectively within the uncertainty ranges
of the forward power Pf2 and the reflected power Pr2. In the
present embodiment, the control device 9 evaluates the
high-frequency measuring device 5 as being reliable only in the
case the forward power Pf1 is within the uncertainty range of the
forward power Pf2 and the reflected power Pr1 is within the
uncertainty range of the reflected power Pr2. Furthermore,
evaluation of reliability is not limited thereto. For example, the
high-frequency measuring device may be evaluated as being reliable
if either the forward power Pf1 or the reflected power Pr1 is
within an uncertainty range. In addition, the high-frequency
measuring device 5 may also be evaluated as being reliable if the
forward power Pf1 is within the uncertainty range or may be
evaluated as being reliable if the reflected power Pr1 is within
the uncertainty range.
[0098] On the other hand, in the case the range of the difference
between forward power Pf3 and forward power Pf4 is narrower, the
control device 9 evaluates reliability of the high-frequency
measuring device 5 based on whether or not the difference between
the forward power Pf1 and the reflected power Pr1 (Pf1-Pr1) is
within the range between the forward power Pf3 and the forward
power Pf4. In the present embodiment, the control device 9
evaluates the high-frequency measuring device 5 as being reliable
only in the case the difference (Pf1-Pr1) is within the range
between the forward power Pf3 and the forward power Pf4.
Furthermore, since the arrangement of the elements of the impedance
conversion device 3 and the arrangement of the elements of the
impedance conversion device 6 are mutually symmetrical, a common
element is used for each element, and the capacitances of
corresponding variable capacitors are adjusted in the same manner,
electrical power consumed by the impedance conversion device 3 and
electrical power consumed by the impedance conversion device 6 have
similar values. Thus, the difference between forward power Pf1 and
reflected power Pr1 (Pf1-Pr1) measured by the high-frequency
measuring device 5 arranged between the impedance conversion device
3 and the impedance conversion device 6 is close to the median
value of the forward power Pf3 and the forward power Pf4. Thus,
measurement accuracy of the high-frequency measuring device 5 may
be evaluated as being within an acceptable range only in the case
the difference (Pf1-Pr1) is within a prescribed range centered on
the median value of the forward power Pf3 and the forward power
Pf4.
[0099] The median value of Pf3 and Pf4 is (Pf3+Pf4)/2. The
applicable median value and the median value of Pf3 and Pf4
respectively become (Pf3+(Pf3+Pf4)/2)/2=(3Pf3+Pf4)/4 and
((Pf3+Pf4)/2+Pf4)/2=(Pf3+3Pf4)/4. For example, the high-frequency
measuring device 5 may be evaluated as being reliable on the case
the difference (Pf1-Pr1) is within the range from (3Pf3+Pf4)/4 to
(Pf3+3Pf4)/4 centered on the median value of Pf3 and Pf4 of
(Pf3+Pf4)/2.
[0100] Furthermore, in the case the width of the uncertainty range
of the difference between forward power Pf2 and reflected power Pr2
is the same as the width of the range between forward power Pf3 and
forward power Pf4, either method may be used for evaluation.
Furthermore, evaluation is carried out using the latter method in
the present embodiment.
[0101] Furthermore, as shown in the equation (6), the absolute
values of the uncertainty of forward power .+-.FPU and the
uncertainty of reflected power .+-.RPU become smaller and the
uncertainty range becomes narrower the smaller the reflection
coefficient .rho.l of the load as viewed from the directional
coupler. Thus, a load having a small reflection coefficient is used
in the case of severely evaluating reliability. In addition, in the
case power consumption of the impedance conversion device 3 and the
impedance conversion device 6 is small, the difference between
forward power Pf3 and forward power Pf4 becomes smaller and the
range between forward power Pf3 and forward power Pf4 becomes
narrower. Thus, in the case of severely evaluating reliability,
power consumption of the impedance conversion device 3 and the
impedance conversion device 6 is reduced, or in other words, the
output electrical power of the high-frequency power supply device 1
is reduced or current flow is reduced.
[0102] Next, an explanation is provided of the procedure for
evaluating reliability of the high-frequency measuring device 5
with reference to the flow chart shown in FIG. 6.
[0103] FIG. 6 is a flow chart for explaining the procedure of the
evaluation method according to the first embodiment. This flow
chart indicates the processing procedure carried out by the control
device 9 in the case of evaluating reliability of the
high-frequency measuring device 5 using the evaluation system A
shown in FIG. 2 in an inspection process of the manufactured
high-frequency measuring device 5.
[0104] As was previously described, adjustment values of the
capacitances C3 and C4 for enabling the impedance conversion device
6 to reproduce a desired complex impedance are set in advance.
First, in the evaluation system A shown in FIG. 2, the adjustment
positions of the variable capacitors VC3 and VC4 of the impedance
conversion device 6 are adjusted to set positions (adjusted to the
adjustment values set for the capacitances C3 and C4), an impedance
as viewed from the input end c of the high-frequency measuring
device 5 towards the side of the reference load 8 is set to a
desired complex impedance (S1), and the high-frequency power supply
device 1 is started (S2). Next, the adjustment positions of the
variable capacitors VC1 and VC2 of the impedance conversion device
3 are adjusted, and an impedance as viewed from the output end a of
the high-frequency power supply device 1 towards the side of the
reference load 8 is adjusted to a characteristic impedance (S3).
This adjustment is carried out by adjusting the adjustment
positions of the variable capacitors VC1 and VC2 so that the
reflected power Pr3 measured by the power meter 2 and the reflected
power Pr4 measured by the power meter 7 are at zero. Furthermore,
operation for carrying out this adjustment is referred to as a
"matching operation" in the following description and in the flow
chart of FIG. 6.
[0105] When the matching operation has been completed, namely when
the reflected power Pr3 and the reflected power Pr4 are at zero,
the forward power Pf1 and the reflected power Pr1 measured by the
high-frequency measuring device 5, and the forward power Pf2 and
the reflected power Pr2 measured by the reference electrical power
measuring device 4 are recorded in memory (not shown) in the
control device 9 (S4). Next, the uncertainty ranges of the forward
power Pf2 and the reflected power Pr2 are respectively calculated
from the pre-calculated uncertainty of the reference electrical
power measuring device 4 (forward power uncertainty .+-.FPU and
reflected power uncertainty .+-.RFU) and the forward power Pf2 and
reflected power Pr2 (S5). The range from Pf2(100-FPU)/100 to
Pf2(100+FPU)/100 is calculated as the uncertainty range of forward
power Pf2, while the range from Pr2(100-RPU)/100 to
Pr2(100+RPU)/100 is calculated as the uncertainty range of
reflected power Pr2. In addition, at this time, the range from
Pf2(100-FPU)/100-Pr2(100+RPU)/100 to
Pf2(100+FPU)/100-Pr2(100-RPU)/100 is calculated as the uncertainty
range of the difference between forward power Pf2 and reflected
power Pr2.
[0106] In addition, when the matching operation is completed,
forward power Pf3 measured by the power meter 2 and forward power
Pf4 measured by the power meter 7 are recorded in memory in the
control device 9 (S6). Furthermore, the order in which step S6 is
carried out is not limited to being carried out after step S5, but
rather may be carried out before step S4 or between step S4 and
step S5.
[0107] Next, a judgment is made as to which of the ranges of the
uncertainty range of the difference between forward power Pf2 and
reflected power Pr2 calculated in step S5 and the range between
forward power Pf3 and forward power Pf4 recorded in step S6 is
narrower (S7). More specifically, this judgment is made by
comparing the width of the uncertainty range of the difference
between forward power Pf2 and reflected power Pr2 with the
difference between forward power Pf3 and forward power Pf4. The
width of the uncertainty range of the difference between forward
power Pf2 and reflected power Pr2 is
Pf2(100+FPU)/100-Pr2(100-RPU)/100-{Pf2(100-FPU)/100-Pr2(100+RPU)/100}=Pf2-
FPU( 1/50)+Pr2RPU( 1/50). For example, in the case
.+-.FPU=.+-.RPU=.+-.5%, the width of the uncertainty range of the
difference between forward power Pf2 and reflected power Pr2
becomes Pf2( 1/10)+Pr2( 1/10). In the case the width of the
uncertainty range of the difference between forward power Pf2 and
reflected power Pr2 is smaller than the difference between forward
power Pf3 and forward power Pf4, the uncertainty range of the
difference between forward power Pf2 and reflected power Pr2 is
judged to be narrower than the range between forward power Pf3 and
forward power Pf4.
[0108] In the case the uncertainty range of the difference between
forward power Pf2 and reflected power Pr2 has been judged to be
narrower than the range between forward power Pf3 and forward power
Pf4 (YES in S7), a judgment is made as to whether or not forward
power Pf1 is within the uncertainty range of forward power Pf2 and
whether or not reflected power Pr1 is within the uncertainty range
of reflected power Pr2 (S8). In the case either forward power Pf1
or reflected power Pr1 is within an uncertainty range (YES in S8),
the high-frequency measuring device 5 is evaluated as being
reliable, and a message indicating that the device has passed
inspection is displayed on a display unit not shown of the control
device 9 (S9). In this case, the high-frequency measuring device 5
is advanced to the next step as an acceptable product. On the other
hand, in the case neither forward power Pf1 or reflected power Pr1
is within an uncertainty range (NO in S8), the high-frequency
measuring device 5 is evaluated as being unreliable, and a message
indicating that it failed inspection is displayed on the display
unit (S10). In this case, the high-frequency measuring device 5 is
subjected to processing such as re-calibration as an unacceptable
product.
[0109] In the case the uncertainty range of the difference between
forward power Pf2 and reflected power Pr2 has been judged to be
narrower than the range between forward power Pf3 and forward power
Pf4 (NO in S7), a judgment is made as to whether or not the
difference between forward power Pf1 and reflected power Pr1
(Pf1-Pr1) is within the range between forward power Pf3 and forward
power Pf4 (S11). In the case the difference (Pf1-Pr1) is within the
range between forward power Pf3 and forward power Pf4, namely in
the case Pf3>(Pf1-Pr1)>Pf4 (YES in S11), the high-frequency
measuring device 5 is evaluated as being reliable and a message
indicating that the device has passed inspection is displayed on
the display unit (S12). On the other hand, in the case the
difference (Pf1-Pr1) is not within the range between forward power
Pf3 and forward power Pf4 (NO in S11), the high-frequency measuring
device 5 is evaluated as being unreliable, and a message indicating
that it failed inspection is displayed on the display unit
(S13).
[0110] Furthermore, although it has been described above that
reliability of the high-frequency measuring device 5 is evaluated
based only on measured values of the high-frequency measuring
device 5 when a single complex impedance is reproduced and the
high-frequency measuring device 5 is connected to a load having
that complex impedance, the present embodiment is not limited
thereto. Reliability of the high-frequency measuring device 5 may
also be evaluated after reproducing a plurality of complex
impedances and judging each impedance. Namely, after making the
judgment of step S8 or step S11, a process consisting of returning
to step S1, setting a different load and judging reliability of the
high-frequency measuring device 5 may be repeated a plurality of
times. In this case, the high-frequency measuring device 5 may be
evaluated as being reliable only in the case measured values of the
high-frequency measuring device 5 have been judged to be reliable
in all judgments. The high-frequency measuring device 5 may also be
evaluated as being reliable in the case the number of times
measured values of the high-frequency measuring device 5 have been
judged to be reliable is equal to or greater than a prescribed
number of times.
[0111] Furthermore, although the above description has explained
the case of presetting each step in the control device 9 and the
control device 9 carrying out each step automatically, the present
embodiment is not limited thereto. Each step may also be made to be
carried out by a worker. In addition, some of the steps may be
allowed to be carried out by a worker, while the other steps may be
carried out automatically by the control device 9.
[0112] Furthermore, reliability of the high-frequency measuring
device 5 may also be evaluated using the same procedure as that
shown in the flow chart other than in an inspection process during
production.
[0113] As has been described above, if the impedance conversion
device 6 is set in advance so that an impedance as viewed from the
input end c of the high-frequency measuring device 5 towards the
side of the reference load 8 becomes a desired complex impedance,
the state in which the high-frequency measuring device 5 is
connected to, for example, an actually used plasma processing
device can be reproduced. Reliability of the high-frequency
measuring device 5 is evaluated based on whether or not the forward
power Pf1 and reflected power Pr1 measured by the high-frequency
measuring device 5 while in this reproduced state is respectively
within the uncertainty range of the forward power Pf2 and the
reflected power Pr2 measured by the reference electrical power
measuring device 4. Namely, the high-frequency measuring device 5
is evaluated as being reliable only in the case both the forward
power Pf1 and the reflected power Pr1 are within the uncertainty
range. Thus, reliability of the high-frequency measuring device 5
used for a load other than that having a characteristic impedance
can be evaluated. As a result, electrical power measured values
measured by the high-frequency measuring device 5 can be guaranteed
to be reliable. In addition, inspection for unacceptable products
can be carried out preferably by evaluating reliability of the
high-frequency measuring device 5 during production of the
high-frequency measuring device 5.
[0114] In addition, a judgment is made as to which of the ranges of
the uncertainty range of the difference between forward power Pf2
and reflected power Pr2 input from the reference electrical power
measuring device 4 and the range between the forward power Pf3
input from the power meter 2 and the forward power Pf4 input from
the power meter 7 is narrower when the reflected power Pr3 input
from the power meter 2 and the reflected power Pr4 input from the
power meter 7 are at zero. In the case the uncertainty range of the
difference between forward power Pf2 and reflected power Pr2 is
narrower, an evaluation is made as to whether or not reflected
power Pf1 and reflected power Pr1 are respectively within the
uncertainty range, while in the case the range between forward
power Pf3 and forward power Pf4 is narrower, an evaluation is made
as to whether or not the difference (Pf1-Pr1) between forward power
Pf1 and reflected power Pr1 is within the range between forward
power Pf3 and forward power Pf4. Thus, reliability of the
high-frequency measuring device 5 is evaluated under stricter
conditions. As a result, the accuracy of measured values measured
by the high-frequency measuring device 5 can be guaranteed at a
higher level. In addition, inspection of unacceptable products of
the produced high-frequency measuring device 5 can be carried out
more severely.
[0115] Furthermore, although the above description of the present
embodiment explained the case of evaluating reliability of the
high-frequency measuring device 5, the present embodiment is not
limited thereto. The present invention makes it possible to
evaluate reliability of an electrical power measuring device other
than the high-frequency measuring device 5 (such as an electrical
power measuring device provided with a directional coupler). In
this case, an electrical power measuring device desired to be
evaluated is arranged in the evaluation system A shown in FIG. 1
instead of the high-frequency measuring device 5, and evaluation is
carried out in accordance with the flow chart shown in FIG. 6.
[0116] Furthermore, although the present embodiment as described
above is configured so that the method used to evaluate reliability
differs based on whether or not the uncertainty range of the
difference between forward power Pf2 and reflected power Pr2 is
within the range between forward power Pf3 and forward power Pf4,
the present embodiment is not limited thereto. For example, the
uncertainty range of forward power Pf2 or the uncertainty range of
reflected power Pr2 may be compared with the range between forward
power Pf3 and forward power Pf4, or both the uncertainty range of
forward power Pf2 and the uncertainty range of reflected power Pr2
may be compared with the range between forward power Pf3 and
forward power Pf4.
[0117] In addition, reliability of the high-frequency measuring
device 5 may also be evaluated based on whether or not the
difference (Pf1-Pr1) is within the range between forward power Pf3
and forward power Pf4 without comparing both ranges. Namely,
processing may proceed from step S6 to step S11 while omitting step
S7 in the flow chart shown in FIG. 6. In this case, the reference
electrical power measuring device 4 can be omitted from the
configuration of the evaluation system A. Conversely, reliability
of the high-frequency measuring device 5 may also be evaluated
based on whether or not forward power Pf1 and reflected power Pr1
are respectively within the uncertainty range of forward power Pf2
and reflected power Pr2 without comparing both ranges. In this
case, since it is no longer necessary to measure forward power Pf3
and forward power Pf4, the evaluation system A can be further
simplified. The following provides an explanation of the case of
evaluating the reliability of the high-frequency measuring device 5
using a simplified version of the evaluation system A in the form
of an evaluation system A' as a second embodiment of the present
invention.
[0118] FIG. 7 is a block diagram for explaining the evaluation
system A' for carrying out the second embodiment of the method for
evaluating reliability of an electrical power measuring device
according to the present invention. Furthermore, in this drawing,
the same reference symbols are used to indicate those elements that
are either identical or similar to elements of the evaluation
system A shown in FIG. 1.
[0119] As was explained in FIG. 1, although the evaluation method
according to the first embodiment consists of evaluating
reliability of the high-frequency measuring device X by using the
stricter evaluation criteria among two evaluation criteria
consisting of the uncertainty range of measured values of the
reference electrical power measuring device Y and the electrical
power measuring range between an output electrical power Pf3 of the
high-frequency power supply E and input electrical power Pf4 input
to the termination resistor Ro, in the evaluation method of the
second embodiment, reliability of the high-frequency measuring
device X is evaluated using only the uncertainty range of
electrical power measured values of the reference electrical power
measuring device Y for the evaluation criterion.
[0120] In the evaluation method according to the second embodiment,
the configuration of the evaluation system can be correspondingly
simplified since the output electrical power Pf3 of the
high-frequency power supply E and the input electrical power Pf4
input to the termination resistor Ro are not measured. In this
sense, the evaluation method according to the second embodiment can
be said to be a simplified version of the evaluation method
according to the first embodiment.
[0121] The evaluation system A' shown in FIG. 7 differs from the
evaluation system A shown in FIG. 2 in that the power meters 2 and
7 and the impedance conversion unit 3 are omitted and that the
function of the control device 9' is simplified.
[0122] The control device 9' controls the evaluation system A'. The
control device 9' evaluates reliability of the high-frequency
measuring device 5 by respectively inputting measured values of
forward power and reflected power from the reference electrical
power measuring device 4 and the high-frequency measuring device 5,
and then displays the evaluation result on a display device not
shown. The control device 9' respectively calculates the
uncertainty ranges from the forward power Pf2 and the reflected
power Pr2 measured by the reference electrical power measuring
device 4, and evaluates reliability of the high-frequency measuring
device 5 based on whether or not the forward power Pf1 and the
reflected power Pr1 measured by the high-frequency measuring device
5 are respectively within the uncertainty range of the forward
power Pf2 and the reflected power Pr2. In the present embodiment,
the control device 9' evaluates the high-frequency measuring device
5 as being reliable only in the case the forward power Pf1 is
within the uncertainty range of the forward power Pf2 and the
reflected power Pr1 is within the uncertainty range of the
reflected power Pr2. Furthermore, evaluation of reliability is not
limited thereto. For example, the high-frequency measuring device 5
may be evaluated as being reliable if the forward power Pf1 or the
reflected power Pr1 is within the uncertainty range. In addition,
the high-frequency measuring device 5 may also be evaluated as
being reliable if the forward power Pf1 is within the uncertainty
range, or may be evaluated as being reliable if the reflected power
Pr1 is within the uncertainty range.
[0123] Next, an explanation is provided of the procedure for
carrying out a method for evaluating the measurement accuracy of
the high-frequency measuring device 5 by using the evaluation
system A' with reference to the flow chart shown in FIG. 8.
[0124] Before evaluating reliability of the high-frequency
measuring device 5, it is necessary to preset the impedance
conversion device 6 so that it is able to reproduce a desired
complex impedance. Since the method of setting the impedance
conversion device 6 is the same as in the case of the evaluation
system A, an explanation thereof is omitted here.
[0125] First, in the evaluation system A' shown in FIG. 7, the
adjustment positions of the variable capacitors VC3 and VC4 of the
impedance conversion device 6 are adjusted to set positions, an
impedance as viewed from the input end c of the high-frequency
measuring device 5 towards the side of the reference load 8 is set
to a desired complex impedance (S21), and the high-frequency power
supply device 1 is started (S22). Next, the forward power Pf1 and
the reflected power Pr1 measured by the high-frequency measuring
device 5 and the forward power Pf2 and the reflected power Pr2
measured by the reference electrical power measuring device 4 are
recorded in memory (not shown) in the control device 9' (S23).
Next, the uncertainty ranges of the forward power Pf2 and the
reflected power Pr2 are calculated from the pre-calculated
uncertainty of the reference electrical power measuring device 4
(forward power uncertainty .+-.FPU and reflected power uncertainty
.+-.RPU) and the forward power Pf2 and reflected power Pr2
(S24).
[0126] Next, a judgment is made as to whether or not forward power
Pf1 is within the uncertainty range of forward power Pf2 and
whether or not reflected power Pr1 is within the uncertainty range
of reflected power Pr2 (S25). In the case either forward power Pf1
or reflected power Pr1 is within an uncertainty range (YES in S25),
the high-frequency measuring device 5 is evaluated as being
reliable, and a message indicating that the device has passed
inspection is displayed on a display unit not shown of the control
device 9' (S26). In this case, the high-frequency measuring device
5 is advanced to the next step as an acceptable product. On the
other hand, in the case neither forward power Pf1 or reflected
power Pr1 is within an uncertainty range (NO in S25), the
high-frequency measuring device 5 is evaluated as being unreliable,
and a message indicating that it failed inspection is displayed on
the display unit (S27). In this case, the high-frequency measuring
device 5 is subjected to processing such as re-calibration as an
unacceptable product.
[0127] Furthermore, although it has been described above that
reliability of the high-frequency measuring device 5 is evaluated
based only on measured values of the high-frequency measuring
device 5 when a single complex impedance is reproduced and the
high-frequency measuring device 5 is connected to a load having
that complex impedance, the present embodiment is not limited
thereto. Reliability of the high-frequency measuring device 5 may
also be evaluated after reproducing a plurality of complex
impedances and judging each impedance. Namely, after making the
judgment of step S25, a process consisting of returning to step
S21, setting a different load and judging reliability of the
high-frequency measuring device 5 may be repeated a plurality of
times. In this case, the high-frequency measuring device 5 may be
evaluated as being reliable only in the case measured values of the
high-frequency measuring device 5 have been judged to be reliable
in all judgments, or the high-frequency measuring device 5 may be
evaluated as being reliable in the case the number of times
measured values of the high-frequency measuring device 5 have been
judged to be reliable is equal to or greater than a prescribed
number of times.
[0128] Furthermore, although the above description has explained
the case of presetting each step in the control device 9' and the
control device 9' carrying out each step automatically, the present
embodiment is not limited thereto. Each step may also be made to be
carried out by a worker. In addition, some of the steps may be
allowed to be carried out by a worker, while the other steps may be
carried out automatically by the control device 9'.
[0129] In the second embodiment as well, reliability of the
high-frequency measuring device 5 used for a load other than that
having a characteristic impedance can be evaluated. In addition,
the evaluation system A' can be made to be a simpler system having
fewer constituent members than the evaluation system A, and
accuracy of electrical power measured values of the high-frequency
measuring device 5 can be evaluated using a simpler method than in
the case of the first embodiment.
[0130] According to the equation (6), the absolute values of the
uncertainty of forward power .+-.FPU and the uncertainty of
reflected power .+-.RPU become smaller and the uncertainty ranges
become narrower in the case the reflection coefficient .rho.l of
the load as viewed from the directional coupler is small. Thus, an
adequately suitable evaluation can be made based only on a judgment
of whether or not values lie within the uncertainty ranges. Thus,
the simpler second embodiment is suitable in cases of evaluating
the accuracy of electrical power measured values of the
high-frequency measuring device 5 used for a load having a small
reflection coefficient .rho.l. Conversely, the uncertainty ranges
become large in the case the reflection coefficient .rho.l of the
load is large. Thus, the first embodiment is suitable for carrying
out evaluations under stricter conditions. In addition, since
reflected power from the load becomes large in the second
embodiment in the case the reflection coefficient .rho.l of the
load is large, the range of output electrical power is restricted
by the allowable range of the high-frequency power supply device 1
relative to reflected power. Thus, the first embodiment is suitable
since reflected power from the impedance conversion device 3 is
adjusted to zero and there are no restrictions on the output
electrical power of the high-frequency power supply device 1.
[0131] The method for evaluating reliability of electrical power
measuring devices according to the present invention is not limited
to the above-mentioned embodiments. In addition, the design of the
specific configuration of each portion of the evaluation system for
the evaluation method according to the present invention can be
modified in various ways.
* * * * *